The UN's investigation into who is behind chemical weapons attacks in Syria "is dead," but Russia is open to efforts by Western powers to establish "a new mechanism," Moscow's UN ambassador has said.

Vasily Nebenzya made the assertion on November 22 after a closed United Nations Security Council meeting to discuss reviving the inquiry after Russia several times vetoed its extension in the last month.

Nebenzya claimed that the UN Joint Investigative Mechanism (JIM), which was supported by most council members and had found Russia's ally Syria responsible for all but two recent chemical attacks it investigated in Syria,"has discredited itself completely."

"But we are ready to talk about establishing a new mechanism that would replace the JIM and do the work in a truly professional, objective, and unbiased manner," Nebenzya said.

The United States and its Western allies say Russia killed the investigative body because it didn't like its findings implicating the Syrian government, which has waged a six-year civil war with rebel groups that has killed more than 330,000 people and displaced millions more.

Russia vetoed two council resolutions proposed by the United States and its allies last week to keep the investigation alive, and this week it rejected a Swedish-Uruguayan extension compromise before the UN council voted on it.

British Ambassador Matthew Rycroft, one of the staunchest supporters of the inquiry, said on November 21 that "we are not going to give up, even if there is no more JIM."

Rycroft said supporters of the investigation are looking into other international justice mechanisms that might replace it.

"It will be possible to do something," he said, "and we are determined to make sure that this gap is closed. We are not going to allow the JIM just to be killed off like this with nothing to replace it."

"That is a crucial building block towards accountability, towards making sure that there is justice for the victims and for the survivors and for their families," Rycroft said.

While the Organization for the Prohibition of Chemical Weapons still is authorized to identify instances in Syria where chemical weapons were used, Rycroft said "we require something whose job it is to look at those reports from the OPCW and to determine which of the parties in Syria is responsible for each use of chemical weapons."

Russia had agreed in 2015 to create the joint UN-OPCW mechanism to identify the perpetrators of chemical weapons attacks in Syria. But it withdrew its support after the team repeatedly fingered Damascus.

Moscow's principle complaint is that the JIM uses evidence gathered by other parties, which it said could be manipulated, rather than obtaining all of its evidence first-hand.

JIM's recent conclusion that Syrian President Bashar al-Assad's air force was responsible for a sarin gas attack on the town of Khan Sheikhun on April 4 that killed nearly 100 civilians particularly rankled Russia.

The attack triggered global outrage as images of dying children were shown worldwide, prompting U.S. President Donald Trump days later to launch missile strikes on the Syrian air base where he said the attack was launched.

But Russia complained the UN team never sampled for evidence in the town of Khan Sheikhun or at the Shayrat air base, and based its conclusions on evidence gathered by other parties, such as rebel groups and the Turkish government, which are avowed enemies of Assad.

The UN team's leader conceded it had not visited Khan Sheikhun, but said it was unsafe to do so because it is controlled by the Syrian affiliate of the Al-Qaeda extremist group.

Nebenzya called the Khan Sheihun investigation "fictitious," and said Russia will demand changes in the way investigations are conducted if any new mechanism is established.

But the U.S. Ambassador to the UN Nikki Haley said she doubted Russia will ever agree to set up independent, objective investigations again.

"Russia will not agree to any mechanism that might shine a spotlight on the use of chemical weapons by its ally, the Syrian regime," she said on November 17.

Uruguay's UN ambassador, Elbio Rosselli, said the council may find a way to keep an investigation going in Syria.

"There are mechanisms to look into these situations of chemical weapons everywhere, not only in Syria," he said. "We'll have to see what can be done. This requires a lot of doing."